A fuel vapor treatment apparatus stores the fuel vapors generated in a fuel tank in a canister and supplies the fuel vapors stored in the canister to an engine when the engine is started. Such a fuel vapor treatment apparatus is described in JP-A-2003-49686.
A summary of a fuel supply apparatus provided with a fuel vapor treatment apparatus described in JP-A-2003-49686 is described with reference to FIG. 7 hereof. FIG. 7 is an explanatory view of the outline of a fuel supply apparatus provided with a conventional fuel vapor treatment apparatus.
A fuel supply apparatus 200 is composed of a fuel tank 201 for holding liquid fuel, a filler pipe 202 for supplying liquid fuel to the fuel tank 201, a fuel pump 203 for discharging liquid fuel inside the fuel tank 201, and a fuel supply tube 206 for supplying liquid fuel discharged from the fuel pump 203 to an injector 205 of an engine 204.
The fuel supply apparatus 200 is furthermore provided with a fuel vapor treatment apparatus 210. The fuel vapor treatment apparatus 210 is composed of a canister 211 for storing fuel vapors by adsorption, a fuel vapor introduction tube 212 for introducing the fuel vapors in the fuel tank 201 into the canister 211, and a fuel vapor supply tube 213 for supplying the fuel vapors inside the canister 211 to an intake system 207 of the engine 204.
In the fuel vapor treatment apparatus 210, the fuel vapors inside the fuel tank 201 is temporarily stored in the canister 211 and is fed from the canister 211 to the intake system 207 by using negative suction pressure generated in the intake system 207 when the engine 204 is started.
The amount of fuel vapors stored in the canister 211 differs depending on the effect of the outside air temperature and the storage state of the fuel vapors produced by the canister 211. For this reason, the feed rate (concentration) of the fuel vapors fed from the canister 211 to the intake system 207 of the engine varies. However, the engine 204 is controlled without consideration for the concentration of the fuel vapors fed to the intake system 207. The combustion state of the engine 204 can vary with the concentration of the supplied fuel vapors. Improvements can be made to more suitably control the engine 204.
The negative suction pressure of the intake system 207 can also fluctuate in accordance with the operating state of the engine 204. When the negative pressure is low, the feed rate of the fuel vapors from the canister 211 to the intake system 207 is reduced. In other words, the rate at which the fuel vapors can be purged (scavenged, released) from the canister 211 to the engine 204 is reduced.
In view of the above, there is a need for method that can more suitably and easily control the engine, and that can more suitably feed fuel vapors from the canister to the engine.